302 J. LeConte— Formation of the Coast Range of California. 



1 : 9. Now as this ratio is the result of hoih compression in one 

 direction and extension in another, it follows that either the 

 compression or the extension would be expressed by the 

 square roots of these ratios. Therefore there has been a 

 crushing together of every 26 to 8 parts into 1 and a corre- 

 sponding extension in another direction of every I part into 

 2*5 to 3. But since the short diameters were horizontal and the 

 long diameters vertical, it is evident that throughout the 

 whole squeezed mass every 2^ to 3 feet were crushed together 

 horizontally into one foot, and every foot of vertical thickness 

 was increased or swelled up to two and a half or three feet. 

 This seems to have taken place principally after, by folding, 

 the strata had taken a veitical position. Therefore by the 

 pressure the strata ivere thinned and extended vertically. No 

 allowance has hitherto been made for this change in the esti- 

 mates of the original thickness of folded strata. 



There are several thoughts suggested by the above which I 

 think worthy of mention. 



1. The position of the nodules, sometimes on the surface of 

 the coal seam, sometimes half buried, and sometimes wholly 

 buried in the coaly matter, clearly proves that at the time 

 when the nodules were first .rolled along and deposited there, 

 the coaly matter was in the condition of very soft semi-liquid peat. 



2. It is well known that slaty cleavage is produced by 

 powerful pressure compressing the once plastic mass in one 

 direction and extending it in another. The absence of slaty 

 cleavage, under precisely these conditions, is evidently due, 

 in the case under discussion, to the fact that the materials are 

 unsuitable for the development of that structure, being far too 

 coarse. If cleavage had been produced, however, the planes of 

 cleavage would have heen parallel to the planes of stratificatwri ; 

 and, therefore, the structure would have been almost undis- 

 tinguishable from, and liable to be mistaken for, a fine lamma- 

 lion structure. 



Now, in many cases this parallelism actually occurs. On the 



foothills of the 'Sierra, especially about Snelling, Hornitos and 



Mariposa, are found fine clay slates beautifiilly fissile with their 



planes apparently perpendicular, but in reality dipping at a very 



high angle to the northeast, i. e., under theVange. These are 



evidently true cleaved slates, and the very thin planes into 



which thev easily split are true cleavage-planes and not lami- 



. Yet I looked in vain for any stripe or other 



-rratification in any other direction. Also Whit- 



.. iGeoL Surv., vol. i, p. 226), and I have myself 



- -these slates pass by insensible gradations into, 



aiiu are even mterstratified with, coareer materials, showing dis- 



